Sustained variable negative pressure wound treatment and method of controlling same

ABSTRACT

Disclosed herein are systems and methods for providing reduced or negative pressure, and more particularly cyclical reduced pressure, to treat a wound. The system can include a wound dressing, a fluid collection container, a suction source, filters, and conduits. In addition, the system can include a control device and sensors. The sensors may be configured to monitor certain physiological conditions of a patient such as temperature, pressure, blood flow, blood oxygen saturation, pulse, cardiac cycle, and the like. Application of cyclical reduced pressure between two or more values below atmospheric pressure may be synchronized with the physiological conditions monitored by the sensors. Certain embodiments of the system utilize an air reservoir and one or more valves and pressure sensors or gauges to allow for rapid cycling of the level of reduced pressure within the wound dressing between two or more reduced pressure values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/570,571, filed Sep. 13, 2019, which is a continuation of U.S. patentapplication Ser. No. 16/009,699, filed Jun. 15, 2018 and now U.S. Pat.No. 10,493,182, which is a continuation of U.S. patent application Ser.No. 14/945,935, filed on Nov. 19, 2015 and now U.S. Pat. No. 9,999,711,which is a continuation of U.S. patent application Ser. No. 13/758,209,filed on Feb. 4, 2013 and now U.S. Pat. No. 9,192,700, which is acontinuation of U.S. patent application Ser. No. 12/812,232, filed onJul. 8, 2010 and now U.S. Pat. No. 8,366,692, which is a U.S. NationalPhase of PCT International Application No. PCT/US2009/030497, filed onJan. 8, 2009, which claims the benefit of U.S. Provisional PatentApplication No. 61/019,819, filed on Jan. 8, 2008. The disclosures ofthese prior applications are incorporated by reference in their entiretyand should be considered a part of this specification.

BACKGROUND OF THE INVENTION Field of the Invention

Certain embodiments of the present application relate to treating awound by applying reduced or negative pressure to the wound.

Description of the Related Art

The treatment of open or chronic wounds that are too large tospontaneously close or otherwise fail to heal has long been atroublesome area of the medical practice. Closure of an open woundrequires inward migration of surrounding epithelial and subcutaneoustissue. Some wounds, however, are sufficiently large or infected thatthey are unable to heal spontaneously. In such instances, a zone ofstasis in which localized edema restricts the flow of blood to theepithelial and subcutaneous tissue forms near the surface of the wound.Without sufficient blood flow, the wound is unable to successfully fightbacterial infection and is accordingly unable to close spontaneously.

An initial stage of wound healing is characterized by the formation ofgranulation tissue which is a matrix of collagen, fibronectin, andhyaluronic acid carrying macrophages, fibroblasts, and neovasculaturethat forms the basis for subsequent epithelialization of the wound.Infection and poor vascularization hinder the formation of granulationtissue within wounded tissue, thereby inhibiting wound healing. Ittherefore becomes desirable to provide a technique for increasing bloodcirculation within wounded tissue to promote spontaneous healing and toreduce infection.

Another problem encountered during the treatment of wounds is theselection of an appropriate technique for wound closure during thehealing process. Sutures are often used to apply force to adjacentviable tissue in order to induce the edges of a wound to migratetogether and heal. However, sutures apply a closure force to only a verysmall percentage of the area surrounding a wound. When there isscarring, edema, or insufficient tissue, the tension produced by thesutures can become great, causing excessive pressure to be exerted bythe sutures upon the tissue adjacent to each suture. As a result, theadjacent tissue often becomes ischemic, thereby rendering suturing oflarge wounds counterproductive. If the quantity or size of the suturesis increased to reduce the tension required of any single suture, thequantity of foreign material within the wound is concomitantly increasedand the wound is more apt to become infected. Additionally, the size ortype of a particular wound may prevent the use of sutures to promotewound closure. It therefore becomes desirable to provide an apparatusand method for closing a large wound that distributes a closure forceevenly about the periphery of the wound.

Wounds resulting from ischemia, or lack of blood flow, are also oftendifficult to heal since decreased blood flow to a wound may inhibitnormal immune reaction to fight infection. Patients that are bedriddenor otherwise non-ambulatory are susceptible to such ischemic wounds asdecubitus ulcers or pressure sores. Decubitus ulcers form as a result ofconstant compression of the skin surface and underlying tissue thusrestricting circulation. Since the patient is often unable to feel thewound or to move sufficiently to relieve the pressure, such wounds canbecome self-perpetuating. Although it is common to treat such woundswith flaps, the conditions that initially caused the wound may also workagainst successful flap attachment. Wheelchair-bound paraplegics, forexample, must still remain seated after treatment of pelvic pressuresores. It therefore becomes desirable to provide a treatment procedurefor ischemic wounds that can be conducted in situ upon an immobile orpartially mobile patient.

Other types of wounds in which ischemia leads to progressivedeterioration include partial thickness burns. A partial thickness burnis a burn in which the cell death due to thermal trauma does not extendbelow the deepest epidermal structures such as hair follicles, sweatglands, or sebaceous glands. The progression of partial thickness burnsto deeper burns is a major problem in burn therapy. The ability tocontrol or diminish the depth of burns greatly enhances the prognosisfor burn patients and decreases morbidity resulting from burns. Partialthickness burns are formed of a zone of coagulation, which encompassestissue killed by thermal injury, and a zone of stasis. The zone ofstasis is a layer of tissue immediately beneath the zone of coagulation.Cells within the zone of stasis are viable, but the blood flow is staticbecause of collapse of vascular structures due to localized edema.Unless blood flow is re-established within the zone of stasis soon afterinjury, the tissue within the zone of stasis also dies. The death oftissue within the zone of stasis is caused by lack of oxygen andnutrients, reperfusion injury (re-establishment of blood flow afterprolonged ischemia), and decreased migration of white blood cells to thezone resulting in bacterial proliferation. Again, it becomes desirableto provide a technique for treating burn wounds by enhancing bloodcirculation to the wounded tissue to inhibit burn penetration. Negativepressure wound therapy has been around for many years and has beenproven to assist with the healing of wounds.

SUMMARY OF THE INVENTION

In some embodiments of the invention, reduced or negative pressure(e.g., below atmospheric pressure) can be used to assist with thehealing of wounds, and can be used in three general modes. The firstgeneral mode is a continuous mode, wherein negative pressure is appliedin a constant manner up to a predetermined pressure, where the negativepressure is held at this level. The second general mode may becharacterized as being intermittent. In the intermittent mode, thenegative pressure is preferably generally applied to the wound and theneither released or disabled, allowing for a gentle or sudden release ofthe pressure back to atmospheric pressure. A variation of theintermittent mode comprises application of the negative pressure to thewound at a first magnitude and then either releasing or disabling thepressure such that the negative pressure reaches a second magnitude.Application of intermittent pressure to the wound can assist patientswith chronic, traumatic, and other type of wounds by healing such woundsin a rapid and efficient manner.

In some embodiments, such wounds are treated by using a negativepressure wound therapy apparatus preferably comprising a wound dressing,a fluid collection device, one or more conduits, filters, a suctionsource (e.g., a vacuum pump) configured to apply cyclical reducedpressure to the wound, and a control device configured to control thesuction source. In some embodiments, cyclical reduced pressure may beapplied to the wound between two or more magnitudes of pressure belowatmospheric pressure and at one ore more frequencies of cycling.

In some embodiments, the apparatus may comprise one or more sensorsconfigured to monitor physiological conditions of a patient, such assuch as temperature, pressure, blood flow, blood oxygen saturation,pulse, cardiac cycle, and the like. In some embodiments, the controldevice may receive the conditions monitored by the one or more sensorand control the suction source based on the monitored conditions.

In some embodiments, the apparatus may be configured to apply cyclicalreduced pressure to the wound in synchrony with the monitored heartactivity of the patient received from the one or more sensors. In someembodiments, the control device may control the suction source to applya reduced pressure at a first amplitude during duration of systolicperiod, and to release the reduced pressure at the first amplitude toapply a reduced pressure at a second amplitude during duration ofdiastolic period. In some embodiments, the control device may controlthe suction source to apply a reduced pressure at a first amplitudeduring duration of diastolic period, and to release the reduced pressureat the first amplitude to apply a reduced pressure at a second amplitudeduring duration of systolic period. In some embodiments, the reducedpressure at the first amplitude may be applied during the entirety ofsystolic period and a part of diastolic period. In some embodiments, thereduced pressure at the first amplitude may be applied during theentirety of diastolic period and a part of systolic period. In someembodiments, cycling between the reduced pressure at the first amplitudeand the reduced pressure at the second amplitude comprises varyingreduced pressure according to a time-varying waveform such as a square,half-wave rectified trapezoid, and triangular waveforms and symmetric,half-wave rectified, asymmetric, and partially rectified asymmetricsinusoidal waveforms.

In some embodiments, the apparatus may be configured to apply cyclicalreduced pressure to the wound in synchrony with the monitored blood flowthrough the wound received from the one or more sensors. In someembodiments, the apparatus may be configured to provide a baselinenegative pressure of approximately 10-12 mmHg below atmosphericpressure, and to cycle the negative pressure by increasing the negativepressure applied to the wound by approximately 20-150 mmHg, at afrequency of approximately 20-60 cycles per minute. In some embodiments,to provide brief sustained levels of greater negative pressure, theapparatus may be configured for a baseline negative pressure ofapproximately 20 mmHg below atmospheric pressure, and for cycling thenegative pressure by increasing it to approximately 200 mmHg belowatmospheric pressure, at a frequency of approximately 120 cycles perminute.

In some embodiments, the apparatus may be configured to apply cyclicalreduced pressure to the wound such that the reduced pressure at thesecond amplitude is between 5 and 85 mmHg above the reduced pressure atthe first amplitude. In some embodiments, the apparatus may beconfigured to cycle the reduced pressure at the first and secondamplitudes with a frequency of 200 to 400 cycles per minute.

In some embodiments, the apparatus can comprise an air reservoir and oneor more valves and pressure sensors or gauges to allow for rapid cyclingof the level of reduced pressure within the wound dressing between twoor more reduced pressure values. The air reservoir, valves, and pressuresensors or gauges may be configured to supply positive pressure to thewound dressing from the air reservoir and reduced pressure to the wounddressing from the suction source. In some embodiments, the apparatus maybe configured to comprise one or more conduits connecting the suctionsource and the air reservoir to the wound dressing. In some embodiments,the apparatus may comprise one or more safety valves.

In some embodiments, the air reservoir can be connected to the suctionsource and the wound dressing, and configured to supply positivepressure to the wound dressing. A control valve may be connected to theair reservoir and the wound dressing, the control valve may beconfigured to circulate air from the air reservoir into the wounddressing. In some embodiments, the apparatus can be configured to applycyclical reduced pressure to the wound by closing the control valveduring application of the reduced pressure at a first amplitude andopening the control valve during application of the reduced pressure ata second amplitude, such that opening the control valve circulates airfrom the air reservoir into the wound dressing.

Other embodiments of the invention are directed to methods for utilizingthe apparatuses described above, and the subcomponents of theapparatuses described above. In one embodiment, a method for treating awound of a patient is provided. A wound dressing is placed over andencloses the wound, the dressing adapted to maintain reduced pressurebetween the dressing and the wound. Reduced pressure is applied to thewound, wherein the applied reduced pressure is cycled between at leasttwo different magnitudes of reduced pressure. In one embodiment, heartactivity of the patient may be monitored, and the cycling issynchronized to the monitored heart activity. In another embodiment,positive pressure may be supplied to the wound dressing from an airreservoir. A control valve may be closed between the air reservoir andthe wound dressing during application of reduced pressure at a firstamplitude, and the control valve may be opened during application ofreduced pressure at a second amplitude, wherein the opening of thecontrol valve circulates air from the air reservoir into the wounddressing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages will now be describedin connection with certain embodiments, in reference to the accompanyingdrawings. The illustrated embodiments, however, are merely examples andare not intended to be limiting. The following are brief descriptions ofthe drawings.

FIG. 1 is a schematic representation of a continuous reduced pressureprogram.

FIG. 2 is a schematic representation of a sustained variable reducedpressure program.

FIG. 3 is a schematic representation of an embodiment of a sustainedvariable negative pressure wound treatment apparatus.

FIG. 4A is a schematic representation of another embodiment of asustained variable negative pressure wound treatment apparatus.

FIG. 4B is a schematic representation of another embodiment of asustained variable negative pressure wound treatment apparatus.

FIG. 5 is a schematic representation of another embodiment of asustained variable negative pressure wound treatment apparatus,illustrating sensors embedded in the wound.

FIG. 6 is a schematic representation of another embodiment of asustained negative pressure wound treatment apparatus, illustratingsensors positioned adjacent to the dressing.

FIG. 7A-7G is a schematic representation of a sustained variablenegative pressure program wherein negative pressure cycling issynchronized to a patient's heartbeat.

FIG. 8 is a schematic representation of a sustained variable negativepressure program wherein negative pressure cycling comprises pulsing.

FIG. 9 is a schematic representation of another embodiment of asustained variable negative pressure wound treatment apparatus,illustrating control, recording, and alarm devices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Negative pressure can be used to assist with the healing of wounds, andin certain embodiments of the invention, can be used in three generalmodes. The first general mode is a continuous mode, wherein negativepressure is applied in a constant manner up to a predetermined pressure,where the negative pressure is held at this level. For example, FIG. 1illustrates continuous application to the wound site of negativepressure 80 mmHg below atmospheric pressure.

The second general mode may be characterized as being intermittent. Inthe intermittent mode, the negative pressure is preferably generallyapplied to the wound and then either released or disabled, allowing fora gentle release of the pressure back to atmospheric pressure. Avariation of the intermittent mode, referred to herein as sustainedvariable negative or reduced pressure, comprises application of thenegative pressure to the wound at a first magnitude and then eitherreleasing or disabling the pressure such that the negative pressurereaches a second magnitude. For example, FIG. 2 illustrates applicationof sustained variable negative pressure to the wound by cycling betweennegative pressure amplitudes of approximately 85 mmHg and 10 mmHg belowatmospheric pressure. As is illustrated in FIG. 2 , negative pressure ofabout 10 mmHg below atmospheric pressure is first applied to the wound.Subsequently, the negative pressure is increased (e.g., spiked) to 85mmHg below atmospheric pressure for a short duration, and then releasedback to about 10 mmHg below atmospheric pressure. Such treatment may beadvantageous when a wound causes a lot of pain or when the healing hasreached a plateau.

In some embodiments, the apparatus preferably provides sustainedvariable negative pressure, which may allow for greater versatility inthe application of negative pressure wound treatment. At least someembodiments of the apparatus are preferably configured to allow amedical practitioner or patient to apply a negative pressure in any ofthe three general modes discussed above, or to switch from one mode toanother during operation. In some embodiments, the cycle frequency andamplitude of sustained variable negative pressure that the apparatus canprovide may be adjusted by a patient or a medical practitioner, or maybe pre-programmed in the apparatus.

Sustained variable negative pressure wound treatment is a new and novelconcept that can assist patients with chronic, traumatic, and other typeof wounds by healing such wounds in a rapid and efficient manner. Forexample, delivery of sustained variable negative pressure can besynchronized to a patient's heartbeat to maintain better blood flowthrough the wound and to promote healing. As another example, deliveryof sustained variable negative pressure can by decreasing the amplitudeof pressure below capillary closing pressure, thus maintaining a higherlevel of blood flow through the wound.

FIG. 3 is a schematic view of an embodiment of a sustained variablenegative pressure wound therapy apparatus 20. As described herein, asustained variable negative pressure wound therapy apparatus may beconfigured to treat a wound by application of reduced pressure (e.g.,below atmospheric pressure) to a wound site 22 at different amplitudesso as to provide sustained variable negative pressure to the wound site22 in a controlled manner for a selected period of time.

As is illustrated in FIG. 3 , the negative pressure wound therapyapparatus 20 comprises a wound cover or wound dressing 24 for enclosinga wound site 22 and providing a fluid-tight or gas-tight enclosure overthe wound site 22 to effect treatment of a wound site 22 with sustainedvariable negative pressure. For the purpose of creating suction withinthe wound dressing 24, the wound dressing 24 is connected to a vacuumsystem 26 to provide a source of suction or reduced pressure for thesealed wound dressing 24 at the wound site 22. The suction source 26 maycomprise a vacuum pump 30 that preferably cycles between at least twopredetermined levels of negative pressure, the negative pressure beingapplied to a wound or wound dressing, wherein the predetermined levelsof negative pressure are greater than zero such that a negative pressureis always applied to the wound or wound dressing. The suction source 26may further comprise a control device 32, a filter 34, and tubing 36that connects the vacuum pump 30 to a fluid collection system 28.Predetermined amounts of suction or reduced pressure are produced by thevacuum pump 30. The vacuum pump 30 is preferably controlled by a controldevice 32 that will be described in greater detail below. A filter 34,such as micropore filter, is attached to the exhaust of the vacuum pump30 to prevent potentially pathogenic microbes or aerosols from the woundsite 22 from being vented to the atmosphere by the vacuum pump 30. Insome embodiments (not shown), the filter may preferably be positionedbetween the fluid collection system 28 and pump 30 along tubing 36 suchthat the pump may be protected from contaminated fluids. In someembodiments, the suction source 26 can comprise two or more vacuum pumps30 (primary and secondary pumps) connected with tubing 36, preferablyarranged in parallel. As described below, the additional pump mayprovide faster switching of reduced pressure cycles, increased suction,and a higher level of safety and product quality by providing pumpredundancy to prevent a suction source failure in the event that asingle pump fails. In some embodiments, the cycle frequency andamplitude of sustained variable negative pressure that the apparatus canprovide can be adjusted by a patient or medical practitioner, or can bepre-programmed in the apparatus. For safety reasons, there may be limitsas to how low or high the frequency and amplitude may be adjusted orpre-programmed.

Between the wound dressing 24 and the suction source 26 is a fluidcollection system 28 for intercepting and retaining exudate that isaspirated from the wound site 22. The fluid collection system 28 ispreferably interconnected between the suction vacuum pump 30 and wounddressing 24 to remove and collect any exudate which may be aspiratedfrom the wound site 22 by the wound dressing 24. The wound dressing 24preferably functions to actively draw fluid or exudate from the woundsite 22. Collection of exudate in a fluid collection system 28 betweenthe vacuum pump 30 and the wound dressing 24 is preferred to preventclogging of the vacuum pump 30.

As illustrated in FIG. 3 , the fluid collection system 28 may becomprised of a fluid-impermeable collection container 38 and a shutoffmechanism 40. The container 38 may be of any size and shape suitable forintercepting and retaining a predetermined amount of exudate. Manyexamples of such containers are available in the relevant art. Thecontainer 38 illustrated preferably has a first port 42 and a secondport 44 positioned on the top of the container 38. The first port 42preferably enables suction to be applied to the wound dressing 24through the tubing 46 and also enables exudate from the wound site 22covered by wound dressing 24 to be drained into the container 38. Insome embodiments, the tubing 46 may comprise two or more tubes, withconstant level of negative pressure and cycled negative pressure beingapplied through different tubes to a wound or wound dressing. In someembodiments, the tubing 36, 46 can be sized and configured to conductenough air to permit the apparatus to rapidly cycle the level of reducedpressure within the dressing 124 between two or more reduced pressurevalues. The container 38 provides a means for containing and temporarilystoring the collected exudate. A second port 44 is also provided on thetop of the container 38 to enable the application of suction from thevacuum pump 30 to the container 38. As mentioned above, the second port44 of the collection system 28 is connected to the vacuum pump 30 by avacuum line 36. The collection system 28 is preferably sealedapproximately gas-tight so that as to enable the suction vacuum pump 30to supply suction to the wound dressing 24 through the collection system28.

The fluid-impermeable wound cover 50 in the embodiment of the wounddressing 24 illustrated in FIG. 3 may be substantially rigid (to bettersupport application of cyclical negative pressure) or flexible sheet.The sheet may also include an adhesive, and may be a fluid impermeablepolymer sheet for covering and enclosing the wound site 22, including anoptional absorbable matrix 48 within it, and the surrounding normal skin50 around the wound site 22. In some embodiments, the wound cover 50 maybe of biologically created material, such as artificially grown skin. Infurther embodiments the matrix 48 may be non-bioabsorbable, as is knownin the art. The wound cover 50 preferably includes an adhesive backing54 which functions to seal the wound cover 50 to the normal skin 52around the periphery of the wound site 22 so as to provide a generallygas-tight or fluid-tight enclosure over the wound site 22. The adhesivecover 50 preferably has sufficient adhesion to form a fluid-tight orgas-tight seal around the periphery of the wound site 22 and to hold thecover 50 in sealed contact with the skin 52 during the application ofsuction, reduced or negative pressure, or cycled negative pressure. Thewound cover 50 also preferably provides a gas-tight seal around thetubing 46 at the feedthrough location 56 where the tubing 46 emergesfrom beneath the wound cover 50. The tube segment 46a embedded withinthe absorbable matrix 48 preferably has at least one side port 58positioned within the interior of the absorbable matrix 48 to enable asubstantially uniform application of reduced pressure throughout theenclosure. In some embodiments (not shown), the tubing 46 may beconnected to the wound dressing 24 through a port positioned on the topof the dressing.

In some embodiments, the wound dressing 24 may also comprise anintermittent layer (not shown) configured to evenly distribute thesuction over the wound. The intermittent layer may contain a variety ofmaterials that partially collapse under application of negativepressure, such as gauze and gauze type materials, open cell foams,sponges, matrix type materials, and the like.

The absorbable matrix 48 can be placed over substantially the expanse ofthe wound site 22 to encourage growth of tissue in the area of the woundsite 22 into the matrix 48 as the wound heals. The size andconfiguration of the absorbable matrix 48 can be adjusted to fit theindividual wound site 22. It can be formed from a variety of absorbablematerials, preferably a material that is also porous. The matrix 48should be constructed in a manner so that it is sufficiently porous toallow oxygen to reach the wound site 22. The absorbable matrix 48 ispreferably constructed of a non-toxic material that is absorbable by theepithelial and subcutaneous tissue within the area of the wound site 22,such as collagens derived from healthy mammals, absorbable syntheticpolymers, or other materials similar to those used for absorbabledressings. However, other materials for and configurations of theabsorbable matrix 48 can be used with the negative pressure woundtherapy apparatus 20 disclosed herein, such as is described in U.S.Patent Application Publication No. US 2004/0073151 A1, which isincorporated by reference herein in its entirety.

In some embodiments, the apparatus may comprise a dressing 24 that isconfigured to distribute the negative pressure approximately evenly toall portions of the wound. Alternatively, in some embodiments theapparatus may comprise a dressing that is configured to distribute thenegative pressure at different levels to different portions of thewound. For example, in some embodiments, if a sensor (as describedbelow) determines that the blood oxygen level flowing into a portion ofthe wound is lower than optimal value, the dressing would preferably beconfigured to provide an increased level of negative pressure to thatparticular portion of the wound. Further as mentioned above, thedressing may have a stronger seal or sealing aspect so as to minimizethe incidence of any leaks in the dressing during the cyclic loading ofnegative pressure.

The suction source 26 can be provided by any suitable device such as,but not limited to, a portable suction pump apparatus, a piston typedevice, several pistons in combination, a diaphragm type pump, a rotaryvane pump, or the like. The suction source can also originate from wallsuction (as is provided in hospitals), and a regulator could be attachedto the wall suction source. As described above, the suction source canbe provided by a vacuum pump. A second pump may be used to providefaster switching of reduced pressure cycles, increased suction, and ahigher level of safety and product quality by providing pump redundancyto prevent a suction source failure in the event that a single pumpfails. Alternatively, a single large volume vacuum pump may be used toprovide switching of reduced pressure cycles and increased suction.Alternatively, the vacuum pump may have a secondary piston or diaphragmthat provides for faster switching of reduced pressure cycles, increasedsuction, and a higher level of safety and product quality.

The vacuum pump may decrease or release the negative pressure appliedduring cycling of negative pressure by releasing the pressure through aport or valve in the pump or in the dressing, or by turning off the pumpsource and allowing inherent leaks in the dressing drop the pressuredown. As shown in FIG. 3 , a valve 33 may be placed along tubing 36 torelease the negative pressure applied during cycling. A filter (notshown), such as micropore filter, may be attached to the port or valveto prevent potentially pathogenic microbes or aerosols from the woundsite 22 from being vented to the atmosphere.

A control device 32 can control the vacuum pump so as to control theamount of suction that is provided to the dressing 24 and wound site.The control device 32 preferably receives signals from the sensors andconverts the signals to an electronic or other suitable form that can berecognized by the vacuum pump. In some embodiments, the control device32 can be configured to operate without a processor. For example, thecontrol circuit and other aspects of the apparatus disclosed inInternational Patent Application Publication No. WO 2008/048481, can beused to control the pump motor or pump described herein. Additionally,any of the configurations described in the above-mentioned WO2008/048481 application publication regarding pressure sensors, thecontrol of such pressure sensors, and/or other aspects of the apparatusdisclosed therein can be used with the apparatus described in thepresent application, and International Patent Application PublicationNo. WO 2008/048481 is hereby incorporated by reference as if fully setforth herein.

In some embodiments, the control device 32 can comprise a processor thatpreferably enables the control device to control the vacuum pump 30 or,as described below, the wound dressing, valves, pressure sensors, orother components comprising the apparatus. Furthermore, the controldevice 32 can be a computer, data processor, or other controller havingany suitable device such as, but not limited to, a processor, forcontrolling the pump motors and/or other components that are describedherein, or for receiving or changing data, or for any other functionsuitable for the apparatus. In some embodiments, a control devicecomprising digital componentry, i.e., comprising digital electronics andmicroprocessors, may improve the robustness of the pump in the sustainedvariable pressure mode.

FIG. 4A is a schematic view of another embodiment of a sustainedvariable negative pressure wound therapy apparatus 120. As illustratedin FIG. 4A, some embodiments of the sustained variable negative pressurewound therapy apparatus 120 can have any of the same components,features, materials, or other details, including but not limited to thefluid collection system, wound cover, wound filler, valves, and/orpressure sensors, as in any other negative pressure wound therapyapparatuses disclosed herein or otherwise known or later developed inthe field.

As will be described in greater detail below, the negative pressurewound therapy apparatus 120 can comprise a wound dressing 124 configuredto cover the wound site 122, a suction source 126, a fluid collectionsystem 128 that can have a collection container 138, a shutoff mechanism140, a first port 142, and a second port 144 positioned on the top ofthe container 138, and an air reservoir 160. As will be described ingreater detail below, the air reservoir 160 can enable the negativepressure wound therapy apparatus 120 to quickly change the level ofreduced pressure within the wound dressing 124 to allow for rapidcycling of the level of reduced pressure within the wound dressing 124.Conduit or tubing 136 can be used to communicate or supply reducedpressure from the vacuum pump 130 to the collection container 138, andconduit or tubing 146 can be used to communicate or supply reducedpressure from the collection container 138 to the wound site 122, bybeing routed under the wound dressing 124. Additionally, conduit ortubing 163 can be used to communicate or supply increased pressure fromthe vacuum pump 130 to the air reservoir 160 and conduit or tubing 166can be used to communicate or supply increased pressure from the airreservoir 160 to the wound site 122, by being routed under the woundcover 124.

As used herein, the term increased pressure is used to describe the airthat is exhausted by the vacuum pump 130 as the vacuum pump 130 reducesthe air pressure within the conduit 136. In some conventional systems orapparatuses, the increased pressure or exhaust air from a vacuum pump istypically exhausted to the atmosphere. In the apparatus 120, however,the increased pressure or exhaust air from the vacuum pump 130 can bedirected into the air reservoir 160 to be used to quickly increase theair pressure within the wound dressing 124 so that the level of reducedpressure within the wound dressing 124 can be cycled between two or morereduced pressure values, as is described herein.

In some embodiments, the suction source 126 can comprise a vacuum pump130 and control device 132. A filter, such as micropore or othersuitable filter (not shown), can be positioned between the vacuum pump130 and the air reservoir 160. The filter can cleanse the exhaust airflowing out of the vacuum pump 130 to prevent or reduce the amount ofbacteria, potentially pathogenic microbes or aerosols, or othercontamination from the vacuum pump 130 exhaust air before the air ischanneled into the air reservoir 160. Additionally, the vacuum pump 130can be configured to vent a portion of the air removed from the conduit136 to the atmosphere. In this configuration, a filter (not shown), suchas a micropore or other suitable filter, can be positioned between thevacuum pump 130 and the atmosphere. The filter can cleanse the exhaustair flowing out of the vacuum pump 130 to prevent or reduce the amountof potentially harmful bacteria or microbes from entering theatmosphere.

Each of the components comprising the suction source 126 can be the sameas or similar to any of the components comprising the suction source ofany other apparatuses described herein or otherwise known or laterdeveloped in the field. In some embodiments, as will be described ingreater detail below, the control device 132 can be configured tocontrol the vacuum pump 130 and any of the valves used in the apparatus120. Additionally, the control device 132 can be configured to receiveand process signal inputs from each of the pressure sensors positionedwithin the apparatus 120, and to control each of the valves and vacuumpump based on, without limitation, the pressure sensor readings andpredetermined reduced pressure loading programs.

A pressure sensor or gauge 137 can be positioned along tubing 136 thatconnects the suction source 126 to the collection container 138. Thepressure sensor 137 can be used to monitor the pressure within theconduit 136. In this configuration, the pressure sensor 137 can be usedto determine the approximate air pressure within the wound dressing 124.Additional valves and pressure sensors can be positioned at any desiredlocation within the apparatus 120 to further monitor and control thepressure within any desired location of the apparatus 120. For example,if desired, additional pressure sensors can be positioned at variouslocations within the apparatus 120 such as, but not limited to, in thetubing 146 connecting the fluid collection system 128 to the wounddressing 124.

A valve 168 can be positioned along tubing 146 as shown. Any of thevalves described herein can be actuated by the control device 132 andcan be used to control the amount of air flow through the conduit inwhich the valve is positioned. As such, the valve 168 can be controlledby the control device 132 to substantially prevent, allow, or otherwisecontrol the level of air flow through the conduit 146. In thisconfiguration, the valve 168 can be used to provide an approximate sealbetween the fluid collection system 128 and the wound dressing 124.

As mentioned, an air reservoir 160 can be connected to the suctionsource 126 with tubing 163. The reservoir 160 can be configured to haveany suitable size, volume, or shape desired. In some embodiments, theair reservoir 160 can be sized and configured to hold enough air topermit the apparatus 120 to rapidly cycle the level of reduced pressurewithin the dressing 124 between two or more reduced pressure values. Thereservoir 160 can have a valve 167, which can vent air from the airreservoir 160 to the atmosphere. The valve 167 can be a safety releasevalve configured to prevent the air reservoir 160 or any othercomponents within the apparatus 120 from rupturing from excessive airpressure. In some embodiments, a filter (not shown), such as microporefilter, may be attached to the valve 167 to prevent potentiallypathogenic microbes or aerosols from the wound site 122 from beingvented to the atmosphere.

A valve 162 can be positioned along the tubing 166 as shown. Asdescribed above, the valve 162 can be configured to control the amountof air flowing through the conduit 166. As such, the valve 162 can beclosed by the control device 132 to provide an approximate seal betweenthe air reservoir 160 and the wound dressing 124. Additionally, a valve164 can be positioned along the tubing 166 as shown in FIG. 4A and canbe used to release the pressure from the wound dressing 124 and thetubing 166. A pressure sensor or gauge 165 can be positioned along thetubing 166 to monitor the pressure in the tubing 166 and, hence, in thewound dressing 124.

An additional pressure sensor (not shown) can be positioned in theconduit 163 or in the air reservoir 160 to monitor the level airpressure between the vacuum pump 130 and the valve 162. This additionalpressure sensor (not shown), can be useful to monitor the level ofpressure within the air reservoir 160 when the valve 162 is closed.Similarly, an additional pressure sensor (not shown) can be positionedwithin the tubing 146 between the wound dressing 124 and the valve 168to monitor the level of pressure within the tubing 146 and, hence, thewound dressing 124, when the valve 168 is closed.

The fluid-impermeable wound cover 150 in the embodiment of the wounddressing 124 illustrated in FIG. 4A preferably provides an approximatelygas-tight seal around the tubing 146 and 166 where the tubing 146 and166 emerges from beneath the wound cover 150. In some embodiments (notshown), one or more of the tubing 146 and 166 may be connected to thewound dressing 124 through a port or ports integrally formed orotherwise attached to the wound cover 150.

In some embodiments, a valve that can be configured to selectivelypermit air to enter the conduit 146 from the atmosphere can bepositioned along the tubing 146 between the valve 168 and the collectioncontainer 138. This valve may be used to quickly provide air to theconduit 146 and, hence, the wound dressing 124 during operation of theapparatus 120 to rapidly decrease the level of reduced pressure withinthe conduit 146 and the wound dressing 124. A filter, such as microporefilter, may be attached to the valve to prevent bacteria, germs,microbes, or other contaminants from the outside air from entering intothe tubing 146 and wound dressing 124.

In some embodiments, a filter, such as micropore or other suitablefilter, can be positioned between the vacuum pump 130 and the collectioncontainer 138 (for example, without limitation, at port 144 or otherwisesupported by the collection container 138) to prevent or reduce theamount of exudate, bacteria, potentially pathogenic microbes oraerosols, or other contamination from the wound site 122 from enteringthe vacuum pump 130. Another filter, such as micropore or other suitablefilter, can be positioned in the tubing 166 to prevent or reduce theamount of exudate, bacteria, potentially pathogenic microbes oraerosols, or other contamination from the wound site 122 from enteringthe vacuum pump 130, and to prevent or reduce the amount of bacteria,potentially pathogenic microbes or aerosols, or other contamination fromentering the wound site 122. The filters described herein mayadditionally be disposable and intended for single patient use.

In some embodiments, the apparatus 120 may be used to provide sustainedvariable negative pressure as follows. With reference to FIG. 2 , point2A represents the level of reduced pressure with wound dressing beforethe suction system 126 has been actuated and, hence, before the pressurewithin the dressing 124 has been reduced. In other words, point 2Arepresents atmospheric pressure. In order to increase the level ofreduced or negative pressure within the wound dressing 124, the valve168 can be opened and valve 162 can be closed when the pump 130 isactuated. Additionally, the valves 164 and 167 can be closed at thispoint to prevent increased pressure from venting to the atmosphere.Thus, in this configuration, when the vacuum pump 130 is actuated, thereduced or negative pressure within the dressing 124 can be increasedfrom point 2A to point 2B (as can be monitored by the pressure sensor137), which is approximately 85 mmHg. Again, the values described hereinand are meant to be approximate and merely exemplifying. As such, thevalues set forth herein are non-limiting. The apparatus 120 or any otherapparatus described herein can be configured to provide any suitable ordesired level of negative or reduced pressure at any suitable or desiredfrequency.

As the pump 130 draws air out of the conduits 136, 146 and, hence,increases the level of reduced pressure within the wound dressing 124from point 2A to point 2B, the air that is drawn out of conduits 136,146 can be channeled into the air reservoir 160. In other words, thelevel of positive pressure within the reservoir 160 can be increasedwith the air that is drawn out of the wound dressing 124, while thelevel of negative pressure in the wound dressing 124 is being increased.Once the level of reduced pressure within the wound dressing 124 hasreached point 2B, the vacuum pump 130 can be stopped and the valve 168can be closed.

In some embodiments, the vacuum pump 130 can be configured such that aircan only flow through the vacuum pump 130 in one direction, tosubstantially prevent air from flowing from the air reservoir 160through the vacuum pump 130 into the conduit 136. Additionally, thevacuum pump 130 can be sized and configured to provide as rapid anincrease in the reduced pressure as is desired. In some embodiments ofthe apparatus 120, multiple vacuum pumps or multi-piston pumps 130 canbe used to increase the rate of air flow through the apparatus 120, sothat the level of reduced pressure within the wound dressing 124 can becycled at any desired amplitude or frequency.

After the level of reduced pressure within the dressing 124 has reachedpoint 2B, the valve 162 can be opened by the control device 132 and thevalve 168 can be closed by the control device 132 or remain closed. Insome embodiments, the valves 162, 168 can be simultaneously opened andclosed, respectively, or the valves 162, 168 can be sequentially openedand closed, respectively. With valve 162 open and a valve 168 closed,positive pressure or air within the air reservoir 160 can be transferredfrom the air reservoir 160 to the volume beneath the wound dressing 124,so as to decrease the level of reduced pressure within the dressing frompoint 2B to point 2C. Consequently, air will be caused to fill theconduit 146 up to the valve 168, causing the level of reduced pressurewithin that portion of the conduit 146 to be decreased to point 2C. Oncethe level of reduced pressure within the volume beneath the wounddressing 124 has reached point 2C, as can be monitored by the pressuresensor 165, the valve 162 can be closed by the control device 132 sothat the level of pressure within the wound dressing 124 is maintainedat approximately point 2C.

Thereafter, the level of reduced pressure within the dressing 124 can bemaintained at a constant level for a period of time (i.e., from point 2Cto point 2D), or it can be approximately immediately increased, such asto the level represented by point 2E. To increase the level of reducedpressure from point 2C or point 2D to point 2E, with the valve 162closed, the vacuum pump 130 can again be actuated and the valve 168 canbe opened, causing the vacuum pump to again draw air from the conduits136, 146 and the volume beneath the wound dressing 124 until the levelof pressure within the wound dressing reaches a desired level, such asthe level represented by point 2E. When this period elapses, the cyclecan repeat as described above. Thus, in this configuration, bycirculating the air through the apparatus 120 as described above, thelevel of reduced pressure within the volume beneath the wound dressing124 can be rapidly cycled.

Additionally, by positioning the valve 168 as close as it is feasible tothe wound dressing 124 and by reducing the volume within each of theconduits, the volume of the negative pressure airspace that is requiredto be increased and decreased can be reduced, thus permitting theapparatus 120 to accommodate higher frequencies of sustained variablepressure. In some embodiments where cycling of negative pressurecomprises small variations in the magnitude of negative pressure (e.g.10 mmHg), the air reservoir 160 may not be needed. In such cases, valve164 may be closed or valve 167 may be opened to not involve thereservoir 160 in the cycling. In some embodiments, the vacuum pump 130may be configured to be reversible, such that the level of reducedpressure within the wound dressing 124 can be increased and decreasedjust by the operation of the vacuum pump 130.

FIG. 4B is a schematic view of another embodiment of a sustainedvariable negative pressure wound therapy apparatus 220. As illustratedin FIG. 4B, some embodiments of the sustained variable negative pressurewound therapy apparatus 220 can have any of the same components,features, materials, or other details, including but not limited to thefluid collection system, wound cover, wound filler, valves, and/orpressure sensors, as in any other negative pressure wound therapyapparatuses disclosed herein or otherwise known or later developed inthe field.

As will be described in greater detail below, the negative pressurewound therapy apparatus 220 can comprise a wound dressing 224 configuredto cover the wound site 222, a vacuum pump 230, a control device 232, afluid collection system 238, and an air reservoir 260. Similar to theair reservoir 160 described above, the air reservoir 260 can enable thenegative pressure wound therapy apparatus 220 to quickly change thelevel of reduced pressure within the wound dressing 224 to allow forrapid cycling of the level of reduced pressure within the wound dressing224. Conduit or tubing 236 can be used to communicate or supply reducedpressure from the vacuum pump 230 to the fluid collection system 238,and conduit or tubing 246 can be used to communicate or supply reducedpressure from the fluid collection system 238 to the wound site 222, bybeing routed under the wound dressing 224. In some embodiments, theconduit 246 can have openings 247 in the end portion of the conduit 246to distribute the pressure within the conduit 246. Additionally, conduitor tubing 263 can be used to communicate or supply increased pressurefrom the vacuum pump 230 to the air reservoir 260 and conduit or tubing266 can be used to communicate or supply increased pressure from the airreservoir 260 to the wound site 222, by being routed under the wounddressing 224. As illustrated in FIG. 4B, the conduit 266 can be joinedwith conduit 248 by using a valve 268 positioned at the juncture ofconduit 248 and 266.

The valve 268 can be controlled by the control device 232 and can beused to permit the conduit 246 to communicate either with conduit 248 orconduit 266, independently. In other words, when the valve 268 is in afirst position, the conduit 246 will be permitted to communicate withthe conduit 248 but not with conduit 266. In this first position, airand/or fluid will be permitted to flow from conduit 246 to conduit 248,but air and/or fluid will not be permitted to flow from conduit 246 orconduit 248 to conduit 266. When the valve 268 is in a second position,the conduit 246 will be permitted to communicate with the conduit 266but not with conduit 248. In this second position, air and/or fluid willbe permitted to flow from conduit 266 to conduit 246, but air and/orfluid will not be permitted to flow from conduit 266 to conduit 246 or248. A valve 270 can be positioned within the conduit 248 to permit orprevent air and/or fluid from flowing through conduit 248. However,valve 270 is not required for the operation of the apparatus 220.

As mentioned above, in the apparatus 220, the increased pressure orexhaust air from the vacuum pump 230 can be directed to the airreservoir 260 to be used to quickly increase the air pressure within thewound dressing 224 so that the level of reduced pressure within thewound dressing 224 can be rapidly cycled between two or more reducedpressure values, as is described herein.

In some embodiments, a filter 234, which can be a micropore or othersuitable filter, can be positioned between the vacuum pump 230 and theair reservoir 260. The filter can cleanse the exhaust air flowing out ofthe vacuum pump 230 to prevent or reduce the amount of bacteria,potentially pathogenic microbes or aerosols, or other contamination fromthe vacuum pump 230 exhaust air before the air is channeled into the airreservoir 260. In some embodiments, a filter (such as, withoutlimitation, filter 234), which can be a micropore or other suitablefilter, can be positioned in the conduit 236 to prevent or reduce theamount of exudate, bacteria, potentially pathogenic microbes oraerosols, or other contamination from the wound site 222 from enteringthe vacuum pump 230. In some embodiments, a micropore or other suitablefilter (such as, without limitation, filter 234), can be positioned inthe outlet port of the collection system 238 or otherwise be supportedby the collection system 238. Additionally, in some embodiments, amicropore or other suitable filter can be positioned between the valve268 and the reservoir 260 to prevent contamination from being circulatedto the wound site 222 and/or from entering the vacuum pump 230.

Additionally, the vacuum pump 230 can be configured to vent a portion ofthe air removed from the conduit 236 to the atmosphere. In thisconfiguration, a filter, such as a micropore or other suitable filter,can be positioned between the vacuum pump 230 and the atmosphere. Thefilter can cleanse the exhaust air flowing out of the vacuum pump 230 toprevent or reduce the amount of potentially harmful bacteria or microbesfrom entering the atmosphere.

In some embodiments, as will be described in greater detail below, thecontrol device 232 can be configured to control the vacuum pump 230 andany of the valves used in the apparatus 220. Additionally, the controldevice 232 can be configured to receive and process signal inputs fromeach of the pressure sensors positioned within the apparatus 220, and tocontrol each of the valves and vacuum pump based on, without limitation,the pressure sensor readings and predetermined reduced pressure loadingprograms.

A pressure sensor or gauge 265 can be positioned so as to be incommunication with tubing 246 that communicates or supplies reducedpressure to the wound site 222. The pressure sensor 265 can be used tomonitor the pressure within the conduit 246 and, hence, the pressurewithin the volume beneath the wound dressing 224. Additional valves andpressure sensors can be positioned at any desired location within theapparatus 220 to further monitor and control the pressure within anydesired location of the apparatus 220. For example, if desired,additional pressure sensors can be positioned at various locationswithin the apparatus 220 such as, but not limited to, in the tubing 266connecting the air reservoir 260 to the valve 268.

As mentioned, an air reservoir 260 can be connected to the vacuum pump230 with tubing 263. The reservoir 260 can be configured to have anysuitable size, volume, or shape desired. In some embodiments, the airreservoir 260 can be sized and configured to hold enough air to permitthe apparatus 220 to rapidly cycle the level of reduced pressure withinthe wound dressing 224 between two or more reduced pressure values. Thereservoir 260 can have a valve 267, which can vent air from the airreservoir 260 to the atmosphere. The valve 267 can be a safety releasevalve configured to prevent the air reservoir 260 or any othercomponents within the apparatus 220 from rupturing from excessive airpressure. In some embodiments, a filter (not shown), such as microporefilter, may be attached to the valve 267 to prevent potentiallypathogenic microbes or aerosols from the wound site 222 from beingvented to the atmosphere.

The fluid-impermeable wound cover 250 in the embodiment of the wounddressing 224 illustrated in FIG. 4B preferably provides an approximatelygas-tight seal around the tubing 246 where the tubing 246 emerges frombeneath the wound cover 250. In some embodiments (not shown), theconduit 246 may be connected to the wound dressing 224 through a portintegrally formed or otherwise attached to the wound cover 250.

In some embodiments, a valve that can be configured to selectivelypermit air to enter the conduit 246 from the atmosphere can bepositioned along the tubing 246 between the valve 268 and the wounddressing 224. This valve may be used to quickly provide air to theconduit 246 and, hence, the wound dressing 224 during operation of theapparatus 220 to rapidly decrease the level of reduced pressure withinthe conduit 246 and the wound dressing 224. A filter, such as microporefilter, may be attached to the valve to prevent bacteria, germs,microbes, or other contaminants from the outside air from entering intothe tubing 246 and wound dressing 224.

In some embodiments, the apparatus 220 may be used to provide sustainedvariable negative pressure as follows. With reference to FIG. 2 , inorder to increase the level of reduced or negative pressure within thewound dressing 224, the valve 268 can be positioned (by the controldevice 232) in the first position so that air can flow from conduit 246into the conduit 248, but not into the conduit 266, when the pump 230 isactuated. Additionally, the valve 270 can be opened to permit air and/orfluid to flow through conduit 248 and into the collection container 238,and the valve 267 can be closed to prevent increased pressure fromventing to the atmosphere. Thus, in this configuration, when the vacuumpump 230 is actuated, the reduced or negative pressure within thedressing 224 can be increased from point 2A to point 2B, which isapproximately 85 mmHg. Again, the values described herein and are meantto be approximate and merely exemplifying. As such, the values set forthherein are non-limiting. The apparatus 220 or any other apparatusdescribed herein can be configured to provide any suitable or desiredlevel of negative or reduced pressure at any suitable or desiredfrequency.

As the pump 230 draws air out of the conduits 246, 248 and, hence,increases the level of reduced pressure within the wound dressing 224from point 2A to point 2B, the air that is drawn out of conduits 246,248 can be channeled into the air reservoir 260. In other words, thelevel of positive pressure within the reservoir 260 can be increasedwhile the level of negative pressure in the wound dressing 224 is beingincreased. Once the level of reduced pressure within the dressing 224has reached point 2B, the vacuum pump 230 can be stopped and the valve270 can be closed.

In some embodiments, the vacuum pump 230 can be configured such that aircan only flow through the vacuum pump 230 in one direction, tosubstantially prevent air from flowing from the air reservoir 260through the vacuum pump 230 into the conduit 236. Additionally, thevacuum pump 230 can be sized and configured to provide as rapid anincrease in the reduced pressure as is desired. In some embodiments ofthe apparatus 220, multiple vacuum pumps or multi-piston pumps 230 canbe used to increase the rate of air flow through the apparatus 220, sothat the level of reduced pressure within the wound dressing 224 can becycled at any desired amplitude or frequency.

After the level of reduced pressure within the dressing 224 has reachedpoint 2B, the valve 268 can be switched from the first position to thesecond position by the control device 232, and the valve 270 can becaused to be closed or remain closed by the control device 232. In someembodiments, the valves 268, 270 can be simultaneously opened andclosed, respectively, or the valves 268, 270 can be sequentially openedand closed, respectively. With valve 268 in the second position so thatair can flow from the conduit 266 to the conduit 246 but not to conduit248, and the valve 270 closed, positive pressure or air within the airreservoir 260 can be transferred from the air reservoir 260 to thevolume beneath the wound dressing 224, so as to decrease the level ofreduced pressure within the dressing from point 2B to point 2C. Once thelevel of reduced pressure within the volume beneath the wound dressing224 has reached point 2C, as can be monitored by air pressure sensor265, the valve 268 can be changed back to the first position so that thelevel of pressure within the wound dressing 224 is maintained atapproximately point 2C.

Thereafter, the level of reduced pressure within the dressing 224 can bemaintained at a constant level for a period of time (i.e., from point 2Cto point 2D), or it can be approximately immediately increased, such asto the level represented by point 2E. To increase the level of reducedpressure from point 2C or point 2D to point 2E, with the valve 268 inthe first position, the valve 270 can be opened, the vacuum pump 230 canagain be actuated, and the valve 268 can be opened, causing the vacuumpump to again draw air from the conduits 246, 248 and the volume beneaththe wound dressing 224 until the level of pressure within the wounddressing reaches a desired level, such as the level represented by point2E. When this period elapses, the cycle can repeat as described above.Thus, in this configuration, by circulating the air through theapparatus 220 as described above, the level of reduced pressure withinthe volume beneath the wound dressing 224 can be rapidly cycled.

Additionally, by reducing the volume within each of the conduits, thevolume of the negative pressure airspace that is required to beincreased and decreased can be reduced, thus permitting the apparatus220 to accommodate higher frequencies of sustained variable pressure.

In some embodiments, the apparatus would preferably enable the medicalpractitioner or patient to set a base level of negative pressure on thewound bed such that there would always be a negative pressure applied tothe wound. Although the apparatus is not limited to the specificnegative pressure ranges described herein, the following are some of thetypical negative pressure ranges that may beneficially promote woundhealing or provide other benefits related to negative pressure woundtherapy and may be used to define either the base level of negativepressure, or the maximum level of negative pressure, that maybe appliedto the wound. For example, in some embodiments the apparatus may beconfigured so as to provide, and so that the dressing can accommodate,up to approximately 200 mmHg of negative pressure below atmosphericlevel. In some embodiments, the dressing and other components of theapparatus can be configured to provide greater than approximately 200mmHg to the wound site, although this level of negative pressure mayexceed the generally desired range for many patients. For someembodiments of the apparatus, it may be desired to provide in excess of200 mmHg of negative pressure to a dressing for purposes of examining adressing, tubing, pump system, or other components of the apparatus forleaks or other performance-based deficiencies or characteristics.

In some embodiments, the apparatus including the dressing can beconfigured to provide as little as approximately 15-80 mmHg of negativepressure to the wound. This level of negative pressure, i.e.,approximately 15-80 mmHg, is typically associated with greater patientcomfort and compliance. Additionally, some embodiments of the apparatusand dressing can be configured to provide and sustain less thanapproximately 15 mmHg at the wound site, although many wounds that aretreated with the apparatus would benefit from a greater level of reducedpressure. Some embodiments of the apparatus can be configured to providenegative pressure levels in excess of approximately 80 mmHg, such aslevels up to approximately 150 mmHg.

As mentioned above, the apparatus is preferably configured to provide apulsed or varying pressure to the wound. The pump would preferablyprovide the pressure through the tubing to the dressing and the wound.In some embodiments, the apparatus may be configured to allow themedical practitioner or patient to vary either the amplitude or thefrequency, or both, of the pulsed or varying pressure to the wound. Asmentioned above, the amplitude of the negative pressure can vary betweenany of the values in any of the ranges described above. In someembodiments, the amplitude of the varying pressure preferably variesbetween two values of negative pressure such that negative pressure isalways provided to the wound. In one non-limiting example, the pumpcould be configured to maintain a minimum level of negative pressure at,for example, approximately 30 mmHg, and cycle the negative pressure upto a higher level of negative pressure, such as up to approximately 80mmHg. In this example, the pump would preferably be configured to cyclethe negative pressure back down to approximately 30 mmHg, whetherthrough a release of pressure through a port or valve in the apparatusor dressing, or merely by turning off the suction source and allowinginherent leaks in the dressing drop the pressure down.

As mentioned, in some embodiments, the apparatus may be configured toallow a medical practitioner or patient to control or vary the frequencyof the cycling between the high and low pressure values. In onenon-limiting example, the frequency of the cycling could range from acycle every approximately 5-10 minutes to a more rapid cycle ofapproximately 180 cycles per minute. This cycling aspect may allow forfaster healing of the wound by stimulating the blood flow.

In some embodiments, the apparatus can comprise sensors such as, but notlimited to, temperature, pressure, blood flow, pulse, cardiac cycle, orblood oxygen saturation sensors. Further, in some embodiments, thesensors can be used to automatically trigger the control device tochange the magnitude or frequency of the pressure cycling based on thedata received from the sensors and pre-programmed algorithms in thecontrol unit used to control the vacuum pump. Accordingly, in someembodiments, when the blood flow rate determined by the blood flowsensor exceeds an optimal or predetermined value, the apparatus can beconfigured so that the amplitude of negative pressure is decreased.Further, in some embodiments, when the blood oxygen saturation leveldetermined by the blood oxygen saturation sensor falls below an optimalor predetermined value, the apparatus can be configured so that theamplitude of the negative pressure is increased, so as to increase bloodflow to the wound.

The sensors can be connected to the control device via leads. The leadsare preferably cables or wires constructed of an electrically conductivematerial, optical fiber, or other suitable medium arranged to enabledata transmission from the sensors to the control device, alarm,recording device, and/or a visual display (not shown). The leads can besealably routed under the wound dressing in a manner that is similar tothat for the tubing so as to maintain the gas and fluid impermeablenature of the seal of the wound dressing to the body. In someembodiments, sensors can transmit information wirelessly so that theleads are not needed.

The sensors and leads are preferably sized and configured so as to notirritate or otherwise damage any of the tissue in or around the woundbed when the wound dressing is changed from the semi-rigid configurationto the collapsed configuration. In some configurations, the sensors andleads may be covered with a cotton gauze or other suitable material thatwill not affect the sensors ability to collect the desired informationfrom the wound bed, but that will protect the wound bed from any damagethat may occur if the sensors or the leads contact the wound bed.

In some embodiments, sensors for surface application (for example, forapplication to the dermis or wound bed) can be used. In someembodiments, sensors that are implantable in the body or otherwiseinvasively applied can be used. In particular, in some embodiments, thesensors can be positioned inside of the wound dressing so as to bepositioned between the wound dressing and the wound. In someembodiments, the sensors can be positioned at least partially within thewound dressing or, in some embodiments, positioned outside of the wounddressing preferably on the surface of or implanted within the healthyskin adjacent to the wound. In some embodiments, the sensors may bepositioned in the wound bed. In some embodiments, only one sensor may bepositioned in the wound bed. Any sensor presently known in the art thatcan be used to measure the parameters disclosed herein or otherparameters of interest may be used with any of the embodiments of theapparatus or wound dressing disclosed herein.

FIG. 5 is a schematic representation of a portion of a sustainedvariable negative pressure wound therapy apparatus 20 in which a pair ofsensors 84 connected to a control device 32 via leads 86 can bepositioned in the wound bed 22. As described above, the wound dressing24 comprises a fluid-impermeable wound cover 50 and can be secured tothe healthy skin surrounding the wound with adhesive (not shown) or byany other suitable method. Either of the sensors illustrated in FIG. 5can be a temperature, pressure, blood flow, pulse, cardiac cycle, orblood oxygen saturation level sensor, or other any other suitable sensorcurrently available or later developed. As illustrated in FIG. 5 , thesensors 84 can be connected to the control device 32 via leads 86. Theleads 86 are preferably cables or wires constructed of an electricallyconductive material, optical fiber, or other suitable medium arranged toenable data transmission from the sensors 84 to the control device 32and alarm device, recording device, and/or a visual display (not shown).The leads 86 can be sealably routed under the wound dressing 24 in amanner that is similar to that for the tubing 46 so as to maintain thegas and fluid impermeable nature of the seal of the wound dressing 24 tothe body.

In some embodiments, one or more sensors can be positioned outside of oradjacent to the dressing. FIG. 6 is a schematic representation of aportion of a sustained variable negative pressure wound therapyapparatus 20 in which a pair of sensors 84 connected to a control device32 via leads 86 can be positioned adjacent to the dressing 24. Either ofthe sensors illustrated in FIG. 6 can be a temperature, pressure, bloodflow, pulse, cardiac cycle, or blood oxygen saturation level sensor, orother any other suitable sensor currently available or later developed.As illustrated in FIG. 6 , the sensors 84 can be connected to thecontrol device 32 via leads 86. The leads 86 are preferably cables orwires constructed of an electrically conductive material, optical fiber,or other suitable medium arranged to enable data transmission from thesensors 84 to the control device 32 and alarm device, recording device,and/or a visual display (not shown). The leads can be routed over thewound dressing 24 as is shown, and can be attached to the dressing. Theleads can be sealably routed under the wound dressing 24 in a mannerthat is similar to that for the tubing 46 as to maintain the gas andfluid impermeable nature of the seal of the wound dressing 24 to thebody. The leads can also be routed through the tubing 46.

In some embodiments, the apparatus may be configured such that thefrequency of the cycling between two or more magnitudes of negativepressure or positive and negative pressure would be synchronized withthe patient's heartbeat or cardiac cycle. Sensors configured to measurethe patient's heartbeat or cardiac cycle at or near the site of thewound or anywhere on the patient's body may be used to enable thesynchronization. Synchronizing the magnitude of the negative pressure tothe patient's heartbeat or cardiac cycle may allow better blood flowthrough the wound and assist with healing. For some patients, thefrequency of the cycling may be between approximately 50-120 cycles perminute, so as to be in synchronization with the patient's pulse.Negative pressure can be cycled in the range of 15-200 mmHg belowatmospheric pressure. In some embodiments, the synchronization of thefrequency of the cycling can be performed by modulating the suctionsource according to the measured patient's heartbeat or cardiac cycle(e.g., an electrical signal).

As mentioned, in some embodiments, a patient's pulse could be determinedwith a pulse sensor, which may be attached to the inside of thedressing, otherwise supported by the dressing, or otherwise positionedin the wound bed. In some embodiments, the pulse sensor could bepositioned adjacent to the wound site. In some embodiments, the pulsesensor could be positioned at another location on the patient's bodypreferably close enough to the wound site so as to provide an accuratereading of the patient's pulse at the wound site. Any sensor presentlyknown in the art or later developed can be used to measure the patient'spulse may be used with any of the embodiments of the sustained variablenegative pressure wound therapy apparatus or wound dressing disclosedherein. Such sensors may include, but are not limited to, invasive ornon-invasive pulse sensors such as pressure transducers, electrodes,photoplethysmographs, and oximeters (e.g., Nonin Medical PulseOximeters, http://www.nonin.com). The patient's pulse can be measured inor adjacent to the wound site, or anywhere on the body. When anotherdevice, such as a pacemaker, implantable cardioverter defibrillator(ICD), pulse oximeter, or the like, measures the patient's pulse, theinformation can be transmitted via leads or wirelessly to the apparatus.

FIG. 7 illustrates application of negative pressure to the wound site bycycling negative pressure synchronized to the patient's cardiac cycle.Each plot illustrates applying greater magnitude of negative pressureduring the systolic period, and decreasing the magnitude of negativepressure during the diastolic period. The plots illustrate applicationof a square (FIG. 7A), half-wave rectified trapezoid (FIG. 7B), andtriangular (FIG. 7C) waveforms and symmetric (FIG. 7D), half-waverectified (FIG. 7E), asymmetric (FIG. 7F), and partially rectifiedasymmetric (FIG. 7G) sinusoidal waveforms. In some embodiments as isshown in FIG. 7D, the application of greater magnitude of negativepressure may not occupy the entirety of the systolic period, andnegative pressure may be released during a portion of the systolicperiod. In order to improve the blood flow to the capillaries, in someembodiments, it may be advantageous to apply greater magnitude ofnegative pressure during the diastolic period, and to decrease themagnitude of negative pressure during the systolic period (i.e., reflectthe plots of FIG. 7 around the x-axis). Application of negative pressurein synchrony with the patient's cardiac cycle may simulate blood pumpingaction within the wound site and/or condition the capillaries and otherblood vessels to open and close at a faster than normal rate to allowfor better blood flow through the wound.

In some embodiments, the apparatus may comprise a pump that allows forincreased blood flow by decreasing the constant pressure on the woundbelow capillary closing pressure. Capillary closing pressure is thepressure that causes blood flow through a capillary to stop. Bydecreasing the constant pressure below this range, a higher level ofblood flow through the capillaries may be maintained. Then the pulsationwith increased amplitude may be applied, drawing this increased bloodflow into the wound itself.

Blood flow sensors configured to measure the blood perfusion through thewound may be used to deliver negative pressure below capillary closingpressure. Any sensor presently known in the art or later developed thatcan be used to measure the flow of blood or the perfusion of red bloodcells into or adjacent to the wound site may be used with any of theembodiments of the apparatus or wound dressing disclosed herein. Suchsensors may include, but are not limited to, the OxyFlo2000, theOxyFlo4000, OxyLab LDF laser Doppler tissue blood perfusion monitors, orlaser Doppler blood flow probes developed by Discovery TechnologyInternational, LLLP (http://www.discovtech.com/PAGE1.htm), any of whichmay be suitable for use with any of the embodiments of the apparatus orwound dressing. Ultrasonic blood flow measurement devices which, in somecases, are based on the laser Doppler technology may also be used tomeasure the flow of blood. Capillary laser Doppler devices that areimplanted within the wound site or adjacent to the wound site mayprovide the most accurate readings of blood flow or the perfusion of redblood cells into or adjacent to the wound site.

In one non-limiting example, the apparatus may be configured to providea baseline negative pressure of approximately 10-12 mmHg belowatmospheric pressure, and to cycle the negative pressure by increasingthe negative pressure applied to the wound by approximately 20-150 mmHg,at a frequency of approximately 20-60 cycles per minute. This isillustrated in FIG. 2 , where the baseline negative pressure at about 10mmHg below atmospheric pressure is applied to the wound. Subsequently,the negative pressure is increased to 85 mmHg below atmospheric pressurefor a short duration, and then released back to the baseline negativepressure. The cycle is repeated at a frequency between 20-60 cycles perminute. In another non-limiting example, to provide brief sustainedlevels of greater negative pressure, the apparatus may be configured fora baseline negative pressure of approximately 20 mmHg below atmosphericpressure, and for cycling the negative pressure by increasing it toapproximately 200 mmHg below atmospheric pressure, at a frequency ofapproximately 120 cycles per minute.

In some embodiments, the apparatus may be configured to provide abaseline negative pressure of approximately 5-60 mmHg below atmosphericpressure, and to cycle the negative pressure by increasing the negativepressure applied to the wound by approximately 5-85 mmHg, at a frequencyof approximately 200-400 cycles per minute. This high frequency levelmay be referred to as micro pulsation. Micro pulsation may condition thecapillaries and other blood vessels to open and close at a faster thannormal rate to allow for better blood flow through the wound. Forexample, FIG. 8 illustrates micro pulsation around a baseline ofapproximately 85 mmHg below atmospheric pressure. The negative pressureapplied to the wound is increased by approximately 5 mmHg below at afrequency between 200-400 cycles per minute.

In another non-limiting example, the apparatus may be configured toprovide a baseline negative pressure of approximately 120 mmHg belowatmospheric pressure, and to cycle the negative pressure to a value inthe range of approximately 10-20 mmHg, at a frequency of approximately10-200 cycles per minute, or even slower at approximately 1-2 cycles infive minutes or, even slower, at approximately 1-2 cycles per day.

Because it is believed that optimal values of the magnitude andfrequency are highly dependent on the patient, in some embodiments, theapparatus may be configured so that the medical practitioner or patientcan adjust the magnitude of the negative pressure and/or the frequencyof the cycling. Thus, in some embodiments, the pump would preferablyhave controls that would enable the amplitude cycling time and durationto be programmed or adjusted.

In some embodiments, the pump would additionally preferably have memorycapacity so as to record data that is provided by any of the sensors inthe apparatus or so as to store programs that control the cycling natureof the negative pressure. For example, in some embodiments, the pumpwould preferably have the ability to sense the oxygen levels, bloodtemperature, pulse, cardiac cycle, or blood flow rate of the woundthrough a variety of sensors. The pump would then preferably be able tocycle through the various typical or non-typical programs that allow forsustained variable pressure to the wound bed and determine which may bethe most optimal for the patient's circumstances and then apply the mostoptimal program to the wound.

It is also highly likely that the body may adapt or that the wound atsome time in the future might need another type of program to optimizethe wound healing process. To account for this, in some embodiments, thepump would preferably have the ability to cycle through the typicalprograms and determine the most optimal program based on oxygen levels,blood temperature, or blood flow rate into the wound, although otherparameters could also be used to determine the most optimal negativepressure program.

As mentioned, the apparatus may comprise a control device, an alarmdevice, and/or other recording device. In some embodiments, however, theapparatus may comprise only the control device. The control devicepreferably receives signals from the sensors and converts the signals toan electronic or other suitable form that can be recognized by the alarmdevice. Accordingly, neither the alarm device nor the recording deviceis required in some arrangements of the apparatus. The alarm device andthe recording device are supplemental components that may be added tothe apparatus to warn the user or practitioner when the valuesdetermined by the sensors exceed predetermined values associated withthe sensors, and to record the values transmitted from the sensors overa predetermined amount of time, respectively. As such, any of theembodiments of the apparatus described herein can operate without theaddition of the alarm device and/or recording device.

With reference to FIG. 9 , the apparatus 20 may comprise a controldevice 32, an alarm device 88, and/or other recording device 90. Thealarm device 88 may produce any type of audible sound when activated,such as a ringing sound, buzzing, chirping or any other common alarmnoise. Alternatively, the alarm device 88 may include a digitallyproduced audible voice that presents pre-arranged messages correspondingto different conditions in the area of the wound site 22. The alarmdevice 88 preferably produces different levels of the alarm dependingupon the magnitude of the measurements received from the sensors 84. Forexample, if the blood flow rate, pulse, cardiac activity, or temperaturedrops below or rises above predetermined values, as measured by thesensors 84, the alarm device 88 may sound successive alarm pitches,sounds, messages or series of sounds. Similarly, as the blood oxygensaturation level measured by any of the one or more sensors 84 fallsbelow or rises above a predetermined value, the apparatus 20 may beconfigured to alert the user. As mentioned above, the control device 32may also control the vacuum pump 30 to adjust the negative pressureunder the wound dressing 24, and the negative pressure under the wounddressing 24 may be adjusted in response to the data collected by thesensors 84.

The recording device 90 may be any device designed to record datareceived from the sensors 84. Such devices are preferably capable ofrecording data on compact disks, DVD disks, floppy disks, magnetic tape,integrated circuits, or other similar media in digital form.Alternatively, the recording device 90 can be a “manual” device thatrecords or displays data through a chart recorder or visual electronicdisplay, such as an LCD or CRT monitor. Such information can be in theform of real-time data, or an average over a predetermined duration oftime, or any other suitable form. In some embodiments, informationregarding the pulse level could be displayed as follows: (i) PulseSteady; (ii) Pulse Increasing; or (iii) or Pulse Decreasing. In someembodiments information regarding blood flow could be displayed asfollows: (i) Blood Flow Steady; (ii) Blood Flow Increasing; or (iii) orBlood Flow Decreasing. Thus, the apparatus 20 or display could embodythis information that is being gathered by one or more of the sensors 84to help with the wound healing as well as provide important informationto a health care practitioner studying the effects of such parameters onwound healing.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the device or process illustrated may be madewithout departing from the spirit of the disclosure. Additionally, thevarious features and processes described above may be used independentlyof one another, or may be combined in various ways. All possiblecombinations and subcombinations are intended to fall within the scopeof this disclosure.

As will be recognized, certain embodiments described herein may beembodied within a form that does not provide all of the features andbenefits set forth herein, as some features may be used or practicedseparately from others. The scope of the inventions is indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A sustained variable negative pressure woundtreatment apparatus comprising: a wound dressing sized and configured tobe placed over and enclose a wound, the dressing adapted to maintainreduced pressure between the dressing and the wound; a suction sourceconfigured to apply cyclical reduced pressure to the wound dressing; acontrol device configured to control the suction source; a sensorconfigured to monitor heart activity of a patient, wherein the controldevice is configured to receive the monitored heart activity from thesensor and control the suction source based on the monitored heartactivity; and a fluid collection device configured to remove and collectfluid and exudate aspirated from the wound by the suction source.
 2. Theapparatus of claim 1, wherein the suction source comprises a vacuumpump.
 3. The apparatus of claim 1, wherein the suction source isconfigured to apply cyclical reduced pressure to the wound between atleast two amplitudes of reduced pressure.
 4. The apparatus of claim 3,wherein the suction source is configured to apply cyclical reducedpressure to the wound by: applying a reduced pressure at a firstamplitude; and releasing the reduced pressure at the first amplitude toapply a reduced pressure at a second amplitude.
 5. The apparatus ofclaim 4, wherein the suction source is configured to apply cyclicalreduced pressure to the wound by cycling between the reduced pressure ata first amplitude and the reduced pressure at a second amplitude.
 6. Theapparatus of claim 1, wherein the control device is configured tocontrol the suction source to apply cyclical reduced pressure to thewound dressing in synchrony with the monitored heart activity receivedfrom the sensor.
 7. The apparatus of claim 6, wherein the control deviceis configured to control the suction source to apply cyclical reducedpressure to the wound dressing in synchrony with the monitored heartactivity received from the sensor by: determining a duration of systolicperiod and a duration of diastolic period; applying a reduced pressureat a first amplitude during the duration of systolic period; andreleasing the reduced pressure at the first amplitude to apply a reducedpressure at a second amplitude during the duration of diastolic period.8. The apparatus of claim 6, wherein the control device is configured tocontrol the suction source to apply cyclical reduced pressure to thewound dressing in synchrony with the monitored heart activity receivedfrom the sensor by: determining a duration of systolic period and aduration of diastolic period; applying a reduced pressure at a firstamplitude during the duration of diastolic period; and releasing thereduced pressure at the first amplitude to apply a reduced pressure at asecond amplitude during the duration of systolic period.
 9. Theapparatus of claim 7, wherein the control device is configured tocontrol the suction source to apply cyclical reduced pressure to thewound dressing in synchrony with the monitored heart activity receivedfrom the sensor by cycling between the reduced pressure at a firstamplitude and the reduced pressure at a second amplitude.
 10. Theapparatus of claim 9, wherein the cycling between the reduced pressureat the first amplitude and the reduced pressure at the second amplitudecomprises varying reduced pressure according to a time-varying waveform.